1. Field of the Invention
The present invention relates to a method of etching a multilevel photoresist layer and, more particularly, to a method of etching a multilevel photoresist layer.
2. Background of the Related Art
To form a semiconductor device, a multilevel photoresist layer is generally used to form a fine pattern if its step coverage is poor. A lower planarizing photoresist layer of the multilevel photoresist layer is generally very thick. Accordingly, its step coverage should be adequate to easily perform the exposure process. The lower planarizing photoresist layer is etched using an intermediate barrier layer of the multilevel photoresist layer as a mask under the condition of higher etch selectivity such that there is no loss of vertical profile and critical dimension (CD).
FIGS. 1A to 1C are cross-sectional views showing a method of etching a photoresist layer in the related art. As shown in FIG. 1A, a layer 12 to be etched is formed on a semiconductor substrate 11, and a first photoresist layer 13 for planarization is formed thereon. An intermediate barrier layer 14 is formed on first photoresist layer 13, and a second photoresist layer 15 is formed thereon.
As shown in FIG. 1B, a second photoresist layer 15 is patterned, and then an intermediate barrier layer 14 is etched using second photoresist layer pattern 15 as a mask. The intermediate barrier layer 14 is etched using fluorine plasma, resulting in a profile as shown in FIG. 1B.
As shown in FIG. 1C, a first photoresist layer 13 is etched using intermediate barrier layer 14, which has been etched, as a mask. The first photoresist layer 13 is dry-etched using an oxygen based process having a higher etch rate to the photoresist layer. However, if only oxygen gas is used for etching first photoresist layer 13, the photoresist layer has isotropic profile due to spontaneous chemical reaction (C+Oxe2x88x92 greater than CO2) between the oxygen gas and photoresist, resulting in severe side etching of the photoresist layer.
To prevent such a problem, a gas such as Ar, Co, SO2, N2O C5H8 (for sidewall passivation of the first photoresist layer) is added to the oxygen plasma when first photoresist layer 13 is etched. Otherwise, the first photoresist layer is etched at a low temperature of below xe2x88x9240xc2x0 C., to thereby induce the sidewall passivation. Thereafter, as shown in FIG. 1D, intermediate barrier layer 14 is removed, and layer 12 is selectively etched using first photoresist layer pattern 13 as a mask.
The above-described conventional method of etching a photoresist layer has various problems. If Ar, Co, SO2, N2O or C5H8 is added to the oxygen plasma for the purpose of inducing the sidewall passivation and vertical profile of the photoresist layer, the intermediate barrier layer is eroded, resulting in a decrease of the etch selectivity of the photoresist layer to the intermediate barrier layer. Further, the etching apparatus must be changed.
An object of the present invention is to substantially obviate one or more of the problems due to limitations and disadvantages of the related art.
Another object of the present invention is to improve the side wall passivation.
Another object of the present invention is to improve the vertical profile results.
Such objects, features and advantages may be achieved at least in part or whole by a method of etching a photoresist layer, in which a photoresist layer is etched using nitrogen gas at a substantially room temperature instead of oxygen gas.
The present invention may be achieved in part or in whole by a method of forming a patterned photoresist layer used for etching a layer on a substrate, comprising the steps of forming a first photoresist layer on the layer; forming a barrier layer on the photoresist layer; patterning the barrier layer; and patterning the first photoresist layer in a nitrogen gas atmosphere using the patterned barrier layer as a mask.
To achieve these and other advantages and in accordance with the purpose of the present invention, the method of etching a photoresist layer includes the steps of sequentially forming a layer to be etched and first photoresist layer on a semiconductor substrate; sequentially forming an intermediate barrier layer and second photoresist layer on the first photoresist layer; patterning the second photoresist layer, and etching the intermediate barrier layer using the patterned photoresist layer as a mask; and etching the first photoresist layer in a nitrogen gas atmosphere, using the intermediate barrier layer patterned as a mask.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims.